1. Field of the Invention
A technology that the present specification discloses relates to a semiconductor device and a method of manufacturing the semiconductor device.
2. Description of Related Art
Japanese Patent Application Publication No 201348230 (JP2013-48230 A) discloses a semiconductor device in which an IGBT and a diode are formed. The IGBT of the semiconductor device includes a barrier region and a pillar region. The barrier region is an n-type region having a high n-type impurity concentration and is formed on the lower side of a body region. The pillar region extends from a top surface of a semiconductor substrate to the barrier region. In the semiconductor device, the body region (p-type) of the IGBT and the barrier region (n-type) of the IGBT form a pn-junction. The pn-junction is made difficult to be turned on by the pillar region. That is, since the barrier region is connected to an upper electrode via the pillar region, a potential of the barrier region is a potential close to a potential of the upper electrode. Even when a voltage by which the upper electrode becomes a higher potential than a lower electrode is applied to the semiconductor device, a high voltage is not applied to the pn-junction described above. Therefore, it is difficult to supply holes from the body region to a drift region. Therefore, in the semiconductor device, a main current flows not through the pn-junction described above but through the pillar region and the barrier region. Thereafter, when an applied voltage is switched to a reverse direction, since the holes in the drift region are discharged to the upper electrode, a current (a backward current with respect to the pn-junction described above) instantaneously flows to the semiconductor device. However, in the semiconductor device, since it is difficult to supply the holes to the drift region, the holes to be discharged to the upper electrode when the applied voltage is switched are scarce, and a backward current is small. Thus, the semiconductor device is excellent in the reverse recovery characteristics.
In the semiconductor device of JP 2013-48230 A, when the IGBT is turned off, a depletion layer expands from the pn-junction of the body region and the bather region to the circumference thereof. At this time, when an n-type impurity concentration in the barrier region is high, the depletion layer broadly extends in the body region. When the depletion layer broadly extends in the body region like this, resistance of the body region becomes high. When the resistance of the body region is high, since the potential of the body region is likely to be high when the IGBT is turned on, a pn-junction between the body region and an emitter region is likely to be turned on As a result, a parasitic npn transistor formed by the emitter region, the body region and the barrier region is likely to be turned on, and the IGBT is likely to cause latch-up.